On the crystal-chemistry of meyerhofferite, CaB3O3(OH)5·H2O

IF 1.2 4区地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY

Physics and Chemistry of Minerals Pub Date : 2022-06-09 DOI:10.1007/s00269-022-01199-1

G. Diego Gatta, Giorgio Guastella, Silvia C. Capelli, Davide Comboni, Alessandro Guastoni

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Abstract

The crystal structure and crystal chemistry of meyerhofferite, ideally CaB₃O₃(OH)₅·H₂O, was investigated by a multi-methodological approach based on titrimetric determination of boron, gravimetric determination of calcium, determination of fluorine by ion selective electrode, determination of water content by heating, other minor elements by inductively coupled plasma atomic emission spectroscopy, along with single-crystal synchrotron X-ray and neutron diffraction. The concentration of more than 50 chemical elements was measured. The combination of these techniques proves that the composition of meyerhofferite approaches the ideal one (i.e., (Ca_1.012Mg_0.003) (B_2.984Si_0.001)O₃(OH)₅·1.018H₂O), with only a modest fraction of Mg (with MgO ≈ 0.03 wt%) replacing Ca, and with Si the only potential substituent of tetrahedral B (with SiO₂ ≈ 0.02 wt%). The content of REE and other minor elements is, overall, not significant, including that of fluorine as a potential OH⁻ substituent (i.e., < 0.01 wt%). These findings have some relevant geochemical and technical implications, here discussed. The X-ray and neutron structure model obtained in this study prove that the building units of the structure of meyerhofferite consist of: two BO₂(OH)₂ tetrahedra and one BO₂(OH) triangle, linked by corner-sharing to form [B₃O₃(OH)₅]²⁻ rings, and distorted Ca-polyhedra (with CN = 8, CaO₃(OH)₄(OH₂)), linked by edge-sharing to form infinite chains along [001]. The B₃O₃(OH)₅ rings are connected to the Ca-polyhedra chains by corner- and edge-sharing, on two sides of the chains. These heteropolyhedral chains, made by Ca-polyhedra and B₃O₃(OH)₅ rings, are mutually connected through hydrogen bonding only, giving rise to the tri-dimensional edifice of meyerhofferite. The neutron structure refinement showed no evidence of static or dynamic disorder pertaining to the H sites; their libration regime was found to be significantly anisotropic. At least seven of the nine oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. The role played by the H-bonding scheme on the physical properties of meyerhofferite is discussed.

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梅氏铁辉石CaB3O3(OH)5·H2O的结晶化学研究

采用硼滴定法、钙重量法、离子选择电极法、加热法测定氟、电感耦合等离子体原子发射光谱法、单晶同步x射线法和中子衍射法等多方法研究了梅氏铁铁矿(CaB3O3(OH)5·H2O)的晶体结构和晶体化学性质。测量了50多种化学元素的浓度。这些技术的结合证明，meyerhofferite的组成接近理想(即(Ca1.012Mg0.003) (B2.984Si0.001)O3(OH)5·1.018H2O)，只有少量Mg (MgO≈0.03 wt%)取代了Ca，而Si是四面体B的唯一潜在取代基(SiO2≈0.02 wt%)。总体而言，稀土元素和其他微量元素的含量并不显著，包括氟作为潜在OH -取代基的含量(即< 0.01 wt%)。这些发现具有一些相关的地球化学和技术意义，在此讨论。本研究获得的x射线和中子结构模型证明，meyerhoverite结构的构建单元包括:两个BO2(OH)2四面体和一个BO2(OH)三角形，通过共享角连接形成[B3O3(OH)5]2 -环，以及扭曲的ca多面体(CN = 8, CaO3(OH)4(OH2))，通过共享边连接形成沿[001]的无限链。B3O3(OH)5环在ca多面体链的两侧通过共享角和共享边连接。这些由ca多面体和B3O3(OH)5环组成的杂多面体链，仅通过氢键相互连接，形成了meyerhoferrite的三维结构。中子结构的细化没有显示出与H位有关的静态或动态紊乱的证据;发现它们的振动状态具有显著的各向异性。该结构的9个氧位点中至少有7个作为供体或受体参与了氢键。讨论了氢键方案对麦氏铁磷灰石物理性质的影响。

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来源期刊

Physics and Chemistry of Minerals 地学-材料科学：综合

CiteScore

2.90

自引率

14.30%

发文量

审稿时长

3 months

期刊介绍： Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)